Cool, Wet Weather with SNOW in the Mountains for the Northwest

The weather over the next few days is going to be shocking for many in the Northwest.

After an extended period with very warm and dry weather, much cooler and quite wet conditions will hit starting later tomorrow.

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But the real stunner will occur in our mountains, with very wet conditions and snow falling above 4000 ft.  So if you are planning on high-elevation recreation this weekend, you should pay attention.

The cumulative rain (purple color) at Sea-Tac airport for the last 12 weeks tells the story.  After a very wet early to mid-April, the spigot turned off over western Washington.  The combination of a wet April and a dry May resulted in the 12-week cumulative rainfall ending up near normal (the cyan line).

And while the last month was dry over western Oregon and Washington, conditions were wetter than normal east of the Cascade crest (see departure of precipitation from normal for the last month below).  Why?  Lots of thunderstorms.

During the next few ways, a deep trough of low pressure will develop over the eastern Pacific, pushing an active front through the region, with cold unstable air behind.  The latest (1 PM) visible satellite image shows a front offshore, followed by lots of convective instability clouds.

By Sunday AM, very cold air will move in aloft.  Here is the forecast for 5 AM Sunday for temperatures at 5000 ft, with blue colors indicating very cool air for this time of the year.

 High temperatures on Saturday and Sunday will only get to 60F, nearly 10F below normal.

Ok, now lets look at the precipitation forecasts.

The total for the 24 hr ending 5 PM Friday, shows substantial rain on the coast, with precipitation just reaching the Cascades.

 The next 24h, ending 5 PM Sunday, predicts lots of precipitation over the western side of the Cascades and substantial amounts in the north Sound as a result of a Puget Sound convergence zone.   Even eastern WA gets rain!

But the fun doesn't end there, on Sunday there will be an influx of cool unstable air produceing lots of showers over the western side of the Cascades and across SW Washington.

With cool air over us on Friday, the snow level will drop quite low---possibly down to 4000 ft (Stevens Pass!).    To illustrate, here is the 24h snowfall ending 5 PM Sunday.   Some snow over the north Cascades and the major volcanic peaks.

 Hiking will not be pleasant over and to the west of the Cascade crest on Saturday and Sunday--so be prepared if you go.    You might even have a chance to throw a snowball!